The preferred embodiments of the present invention generally relates to improvements in a medical X-Ray imaging system, and more particularly relates to an improved positioning control for positioning an imaging X-Ray tube.
FIG. 1 illustrates an exemplary medical X-Ray imaging system 100. The imaging system 100 includes a X-Ray tube 110, a collimator 120, a table detector 130, an X-Ray table 140, a patient 150, and a clinical operator 160. In operation, a patient 150 to be imaged is placed upon the X-Ray table 140 as shown. A clinical operator 160, such as a radiologist or technologist, then positions the X-Ray tube 110 and collimator 120 at one of several pre-determined positions relative to the patient. Once the clinical operator has positioned the collimator 120 at the desired position, the X-ray tube 110 is energized and emits X-Rays. The X-Rays pass through the collimator 120 which directs the X-Rays through the patient to the table detector 130. The energy of the X-Rays passing through the patient is attenuated by the anatomical features of the patient 150. The table detector 130 detects the energy of the X-Rays and develops an image of the anatomical features of the patient 150.
The X-Ray tube 110 and collimator 120 are typically fixed together to form an X-Ray assembly and are typically able to move in three dimensions relative to the X-Ray table 140. That is, the collimator 120 may be moved upward or downward along the patient""s 150 body, right to left across the patient""s 150 body, and closer to or farther from the patient""s 150 body in any of several fixed positions called detents. Each of the several fixed positions or detents may correspond to different X-Ray exposure and imaging parameters that have been predetermined in order to produce the clearest possible images of the patient 150. For example, placing the collimator 120 farther from the patient may result in a different parameter for dynamic range of energy of the X-Rays received by the detector 130.
Typically, imaging parameters are calibrated only for the several predetermined fixed positions, and not continually throughout the path of movement of the collimator 120. That is, the imaging parameters are typically configured for only a single, specific position, and may change rapidly as the collimator is moved. Thus, precise positioning of the collimator 120 helps provide clearer, more clinically relevant images of the patient 150.
Referring to FIG. 1, typically, an medical X-Ray imaging system may employ and configure detents to identify the several fixed imaging positions for radiographic examinations. As the collimator 120 is moved to one of several fixed imaging positions, a detent is engaged which holds the collimator 120 in the desired position while imaging takes place. Detents may be mechanical or electrical, however, detents employing electromagnetic locks and a position reference triggering device may preferably be employed because of, for example, better wear properties.
Positioning errors as small as a millimeter may significantly reduce the quality of the resulting image. For example, anatomical cutoff may occur due to misalignment or misregistration of the beam with respect to the detector. Improving positioning control of the X-Ray tube also aids in the repeatability of X-Ray images which may be of great importance in comparing X-Ray images taken at time intervals during a patient""s treatment. Thus, a need exists for an improved X-Ray tube and collimator positioning system for a medical imaging system.
The preferred embodiments of the present invention provide a system for reducing positioning errors of an X-Ray tube in an X-Ray imaging device. The system facilitates the accurate and repeatable positioning of the X-Ray tube at detents. A preferred embodiment of the present invention preferably includes a sensor unit generating positional or velocity signals indicative of the position or velocity of the X-Ray tube and a microprocessor receiving the positional signals and determining an overshoot correction. The overshoot correction is then used by the X-Ray system to control a locking system controlling the position of the X-Ray tube. The sensor unit may employ a potentiometer, a digital encoder, or preferably both in combination to determine the positional or velocity signals.